Method of fixing photographically exposed oxygen-sensitive free radical photosensitive film



3,351,467 Patented Nov. 7, 1967 fiFice METHGD F FIXHNG PHOTOGRAPHICALLYE"- PQSED @XYGEN SENSHTHVE FREE RADHJAL PHOTUSENSHTHVE FiLM Robert E.Sprague, Chagrin Fails, John A. Stewart, Parma, and James M. Lewis,Cleveland, Ohio, assignors to Horizons Incorporated, Cleveland, Ohio, :1corporation of New .lersey No Drawing. Filed Get. 10, 1363, Ser. No.315,357

8 Claims. (Ci. 96--48) This invention relates to free radicalphotography of the type described in any of the following United Statespatents and in other patents nad pending patent applications directed tophotographic processes of a similar nature:

US. Patent 3,082,086, issued Mar. 19, 1963 US. Patent 3,102,027, issuedAug. 27, 1963 US. Patent 3,102,810, issued Sept. 3, 1963 US. Patent3,104,973, issued Sept. 24, 1963 More particularly, it relates toimprovements in the fixing of the image-bearing film resulting when freeradical compositions such as those described in said patents arephotographically exposed.

As described in the above noted patents and in articles published inPhotographic Science and Engineering, two methods of fixing the exposedimage-bearing free radical films have previously been utilized. In one,the film has been heated after exposure, the amount of heat beingsufficient to drive off at least one essential reactive constituent fromthe film. This method has proven effective with com-positions based ondiphenylamine and carbon tetrabromide such as those described inPhotographic Science and Engineering, vol. 5, No. 2, pp. 98-l03,March-April 1961, and in United States Patent 3,042,515 or withcompositions based on N-vinylcarbazole and carbon tetrabromide such asthose described in United States Patent 3,042,517 and also withcompositions such as those described in United States Patent No.3,121,632, in which a ketone or an organic acid is used to activatecertain types of leuco compounds such as leuco Opal Blue, but it has notbeen found useful with some other types of compositions, particularlythose which exhibit a marked tendency to fog in the unexposed areas whensubjected to heat.

The second method of fixing described in the above disclosures involvesthe application of a solvent rinse which extracts the unexposedcolor-producing reactants from the film composition and leaves the imagedye in the film. Although this method is satisfactory for fixing imagessuch as those produced by the processes described in United StatesPatents 3,095,303 and 3,096,144 and others wherein the dye formingcomponent is colored, the solvent rinse procedure has the disadvantagethat it is a wet process and that in order to have a clean background itis often necessary to perform several rinses which adds to the expenseand time required for processmg.

The present invention is directed to an entirely different method offixing and resides in the discovery that certain free radicalphotographic systems were found to require the presence of oxygen as anessential reactant in the propagation steps of the dye forming chainreaction. The fixing method of the present invention consists of theapplication of a solution containing a plastic film-former and an agentwhich penetrates into the photosensitive layer and which destroys orinhibits the effect of any oxygen already present in the photosensitivefilm and which produces a barrier which effectively prevents thediffusion of oxygen into the photosensitive film. The agent will bedesignated as an inhibitor in the description which follows but it isnot intended that the use of this term shall be construed as alimitation on the invention.

The solution of film-forming plastic: and inhibitor may be sprayed ontothe photosensitive layer or it may be applied thereto by an applicatorbar or by a doctor-knife blade as in any of a number of commerciallyavailable film coating or processing machines. Since volatile solventsmay be used for the fixing overcoat-solution, the applied coating driesvery quickly and for all practical purposes is effectively a dry processfor fixing.

While not wishing to be bound by any specific theoretical reasoning, itappears that this method of fixing is applicable only to those freeradical photosystems which depend on the presence of oxygen in thecolor-forming chain reaction. The single exception to thisgeneralization appears to be those photosensitive compositions in whicha leucoxanthene compound is activated by carbon tetrabromide. Suchcompositions are effectively fixed by the application of theinhibitor-plastic as hereinafter described, although the photographicoperability of these compositions presently is believed to beinsensitive to oxygen. However, this generalization excludes the methodof fixing herein-after described from use in such free radicalphotosystems as the diphenylamine/CBn; system described in US.3,042,515, the styryl dye base/CBn; system described in US. Patent3,095,303 and the cyanine dye base/CBr, system described in US. Patent3,100,703. Furthermore, the method of fixing which constitutes thepresent invention cannot be used in the latent image photosysternsutilizing N-vinylcarbazole and CBr for example, wherein the visibleimage is developed by means of heat as described in United States Patent3,042,517.

The compositions found to be effective for the purposes of thisinvention consist of three essential constituents, namely:

(1) An inhibitor,

(2) A film-forming plastic, and

(3) A solvent for the inhibitor and the film-forming plastic.

It is to be understood that more than a single inhibitor may be used,and that either the solvent or the film-forming plastic may consist ofmore than a single d. compo 1) INHIBITOR In the fixing overcoatings ofthis invention following compounds have been found to be effective asinhibitors:

Hydroquinone Benzoquinone Ascorbic acid l-phenyl-3-pyrazolidone2,6-di-t-butyl-p-cresol 2,6-di-t-butylphenolN,N-diphenyl-p-phenylenediamine Ferric chloride Cobalt chloride Cobaltnaphthenate Cobaltous thiocyanate (2) FILM-FORMING BINDER Anyfilm-forming binders may be used as the basis of the fixing overcoat, itmerely being necessary that the binder does not react chemically withthe inhibitor, for which it is to serve as a physical support, andfurther that a relatively volatile solvent or mixture of such solventsbe available for placing the binder and the inhibitor in solution.

Film-forming binders which have been found useful in the practice ofthis invention include the following:

Polystyrene, Polyvinyl chloride,

Polyvinylidene chloride, Methyl methacrylate, Half-second celluloseacetate, Butyrate,

Cellulose nitrate, and Polycarbonates.

(3) PROPORTIONS The relative proportions of solvent, film-forming binderand inhibitor in the fixing coating solution do not. appear to becritical except that the amount of inhibitor present in the coatingafter the solvent has evaporated or has been otherwise dissipated, mustsuflice for the desired fixing of the photosensitive composition beneaththe fixing layer. While this may depend in some measure on the specificconstituents in the photosensitive layer, it has been found thatinhibitor concentration between 0.1% and 50% by weight in the driedovercoating film provide satisfactory protection against subsequentfogging.

The photosensitive compositions to which the instant invention has beenfound to be particularly applicable include those based on at least oneleuco compound of the type illustrated in list A which follows and atleast one activator of the type listed in list B which follows.

LIST A wherein each R represents a monovalent radical selected from thegroup consisting of diethyl N-, dimethyl N-, methyl ethyl N- and similardi-lower alkyl N-groups; Z

is a member selected from and 8; Q is a member selected from the groupand N-H and wherein R represents a monovalent radical selected from thegroup consisting of methyl, ethyl, n-propyl,

when Z is oxygen and Q represents a member selected from the groupconsisting of NH and CH when Z is sulfur.

LIST B Z-mercaptobenzothiazole 2-mercapto-4-phenylthiazole2-mercapto-fi-naphthothiazole mercaptobenzoic acidot-mercaptoacetaniline Rhodanine 1,3 -diphenylpyrazolone1-phenyl-5-mercaptotetrazole The following examples are intended toillustrate the practice of this invention and are not to be construed aslimiting the same. In the examples all percentages are by Weight unlessotherwise specified.

(31. Example 1 A light-sensitive film was prepared by coating a mixtureof 50 milligrams of3,6-tetramethyldiamino-9-(pdimethylaminophenyl)xanthene and mg.2-mercaptobenzothiazole in 2 cc. acetone plus 2 cc. of 10% polystyrenein benzene. This mixture was coated 0.0015- inch wet thickness onpolyester film, using the drawdown Bird applicator, and allowed to dry.A projection print was made on the film through a silver microfilmnegative in a SOO-watt slide projector with an exposure of 15 seconds ata distance of 45 inches. The exposure produced an intense red print outimage in the light-struck areas against a nearly colorless background inthe unexposed part of the film.

A fixing solution composed of 50 mg. of ferric chloride dissolved in 2cc. of acetone plus 2 cc. of a 10% solution of half-second celluloseacetate butyrate in acetone was applied to the exposed film by adrawdown technique, using the same Bird applicator which had been usedfor the original coating.

Half of the exposed film was covered with the fixing solution in thethis fashion, the other half was left unprotected. After drying, thewhole sheet was re-exposed for 5 minutes to the light of one reflectorphotoflood lamp at 12 inches distance; in the area protected by theferric chloride plastic overcoat very little fogging occurred, while theunprotected area was turned dark purple, with no trace of the imageremaining.

Example 2 A light-sensitive film was prepared and exposed in the samefashion as in Example 1, and a protective overcoat was applied,consisting of 50 mg. of hydroquinone dissolved in 2 cc. of acetone plus2 cc. of 10% halfsecond cellulose acetate butyrate. The protected printwas stable on re-exposure for one minute to a photoflood lamp at 12inches distance, but fogged somewhat on 5- minutes exposure.

Example 3 A light-sensitive film was prepared by coating 2. mixture of25 mg. of 2-mercaptobenzothiazole, 25 mg. of omercaptobenzoic acid and100 mg. of 2,6-tetramethyldiamino-9-(p-dimethylaminophenyl)xanthene in 2cc. acetone plus 2 cc. of 10% polystyrene in benzene, 0.0015- inch wetthickness on polyester film.

The dried film was exposed for 3 seconds through a silver microfilmnegative in a SOO-watt slide projector at a distance of 45 inches, andhalf of the exposed film was topcoated 0.0015-inch wet thickness with asolution of 50 mg. ferric chloride in 2 cc. acetone plus 2 cc. of 10%half-second cellulose acetate butyrate in acetone.

The topcoated area was only slightly fogged on reexposed for 5 minutesto one reflector photoflood lamp at 12 inches distance, while theunprotected area was completely fogged.

Example 4 A photosensitive film was prepared by coating a mixture of 100mg. of 3,6-bis(tetraethyldiamino)-9-(m-nitrophenyl)xanthene and 100 mg.of Z-mercaptobenzothiazole 1n 2 cc. of acetone plus 2 cc. of 10%polystyrene in benzene, 0.0015-inch wet thickness on baryta-coatedpaper. A projection print was made on this paper through a silvermicrofilm negative in a SOO-Watt slide projector at a distance of 45inches with an exposure time of 30 seconds.

Part of the exposed sheet was topcoated 0.0015-inch wet thickness with asolution of 50 mg. of ferric chloride in 2 cc. of acetone plus 2 cc. ofhalf-second cellulose acetate butyrate (10% in acetone). The entiresheet was then re-exposed for 5' minutes to a photoflood lamp at adistance of 12 inches. The topcoated area was only slightly fogged bythis re-exposure, while the unprotected area was changed to a deeppurple-blue color which completely obscured the image.

Example 5 A photosensitive film was prepared in the same fashion as inExample 4 except that the leucoxanthene compound was replaced by 100 mg.of leuco Opal Blue (tris-panilinotriphenylmethane). The dried film wasexposed for one minute to a silver negative to the light from onereflector photoflood lamp at 12 inches distance. Half of the printprepared in this manner was topcoated with the stabilizing solutioncomposed of 50 mg. of ferric chloride dissolved in 2 cc. acetone plus 2cc. of 5% polystyrene in benzene. The coating was applied 0.0015-inchwet thickness, and the film was allowed to dry.

The topcoated area showed very little fog on re-exposure for 5 minutesto one photoflood lamp at 12 inches distance, while the uncoated,unprotected area was completely fogged.

Example 6 A light-sensitive film was prepared in the same fashion as inExample 1. The dried film was exposed for 5 seconds to a silver negativeon a 500-watt slide projector at 45 inches distance, and part of theexposed film was topcoated 0.0015-inch wet thickness with a solution ofone drop of cobalt naphthenate in 2 cc. acetone plus 2 cc. 10%polystyrene in tetrahydrofuran. After re-exposing for 5 minutes to onephotofiood lamp at 12 inches distance there was very little fogging inthe topcoated area while the unprotected part of the film was completelyfogged.

In general, any of the other binders listed previously may besubstituted for polystyrene or half-second cellulose acetate butyrate.Ferric chloride and cobalt naphthenate are the preferred inhibitors foruse in this method of fixing.

It should be particularly noted that the present invention is not to beconfused with the procedure described in Wainer US. Patent 3,042,515 inwhich the use of certain polyhydric phenols and aminophenols isdescribed in connection with the stabilization of free radical filmswhich are subsequently to be fixed by heat. Although it has been foundthat some of the phenolic compounds are operable in the instantinvention, their effectiveness is significantly lower than theeffectiveness of the iron and cobalt compounds hereinbefore described.

We claim:

1. A photographic method which comprises preparing an oxygen sensitivefree radical photosensitive film, photographically exposing said filmand thereafter applying a protective layer to at least one surface ofsaid imagebearing photographically exposed film, said protective layerconsisting essentially of a film-forming plastic and an inhibitorselected from the group consisting of ferric chloride, cobalt chloride,cobalt naphthenate and cobaltous thiocyanate dispersed throughout saidfilm-forming plastic.

2. The method of claim 1 wherein the protective layer is applied as asolution consisting of a film-forming plastic, an inhibitor and avolatile solvent in which said filmforming plastic and said inhibitorare dissolved.

3. The method of claim 2 in which the solution is applied as a wetcoating onto a photographically exposed film and the protective layer isformed by elimination of the solvent.

4. The method of claim 2 in which the solution is sprayed ontothesurface of a photographically exposed film.

5. A method of fixing the image in an oxygen-sensitive photographicallyexposed free radical photosensitive film which consists in applying aprotective layer to at least one surface of said image-bearingphotographically exposed film said protective layer consistingessentially of a film-forming plastic and an inhibitor selected from thegroup consisting of ferric chloride, cobalt chloride, cobalt naphthenateand cobaltous thiocyanate dispersed throughout said film-formingplastic.

6. The method of claim 1 wherein the amount of inhibitor present in saidlayer is about 1 part by weight per 10 parts by weight of film-formingplastic.

7. A laminate comprising an oxygen sensitive, free radicalphotosensitive composition in the form of a thin layer and a protectivecoating which prevents the intrusion of oxygen into the photosensitiveconstituents in said layer, consisting essentially of an inhibitorselected from the group consisting of ferric chloride, cobalt chloride,cobalt naphthenate and cobaltous thiocyanate dispersed in a thin layerof a film-forming binder, said coating being applied to at least onesurface of said oxygen-sensitive film.

8. The laminate of claim 7 wherein the photosensitive compositionconsists essentially of a leuco compound selected from the groupconsisting of leuco xanthenes, leuco thiazines and leuco triarylmethanedyes and an activator for said leuco compound.

References Cited UNITED STATES PATENTS 3/1960 Ryskiewicz 4/1964 Agruss

1. A PHOTOGRAPHIC METHOD WHICH COMPRISES PREPARING AN OXYGEN SENSITIVEFREE RADICAL PHOTOSENSITIVE FILM, PHOTOGRAPHICALLY EXPOSING SAID FILMAND THEREAFTER APPLYING A PROTECTIVE LAYER TO AT LEAST ONE SURFACE OFSAID IMAGEBEARING PHOTOGRAPHICALLY EXPOSED FILM, SAID PROTECTIVE LAYERCONSISTING ESSENTIALLY OF A FILM-FORMING PLASTIC AND AN INHIBITORSELECTED FROM THE GROUP CONSISTING OF FERRIC CHLORIDE, COBALT CHLORIDE,COBALT NAPHTHENATE AND COBALTOUS THIOCYANATE DISPERSED THROUGHOUT SAIDFILM-FORMING PLASTIC.